<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
</head>
<style>
  div{
    width: 300px;
    background-color: rgba(0,0,0,.3);
    position: relative;
    padding: 10px;

  }
  #t1{
    width: 260px;
    padding: 10px 20px;
    border: none;
  }
  img{
    position: absolute;
    right: 30px;
    top: 14px;
  }
  p{
      font-size: 12px;
      color: red;
      margin: 0;
  }


</style>
<body>
<div>

  <input type="text" placeholder="请输入用户名" id="t1">
  <img src="http://doc.canglaoshi.org/tstore_v1/images/login/yhm.png" alt="">
  <p>用户名不能为空</p>

</div>
</body>
</html>